To lower the temperature due to heat generated from a light emitting element such as an LED or the like, and to give sufficient durability for practical use, high heat dissipation characteristics are required for circuit boards on which light emitting elements are mounted. The required heat dissipation characteristics differ according to the light emitting efficiency of the light emitting elements, the input power, and the mounting density, but with high mounting density applications, a metal-base high heat dissipation substrate that performs heat dissipation through a metal plate in a form insulated from electrical circuits is generally used.
For example, Japanese Laid-Open Patent Application (translation of PCT application) No. 2011-507235 discloses a laminate and a flexible substrate structure, the laminate including a copper or aluminum metal layer, a polyimide layer or adhesive agent layer adjacent to the metal layer, a copper thin layer, and a liquid or film solder mask layer. Also, Japanese Laid-Open Patent Publication No. 2003-071982 discloses a thermal countermeasure copper clad plate for which a thin-layer polyimide, having imide units with a specific chemical structure, is laminated and integrated on both surfaces of a low thermal expansion substrate polyimide layer, and for which copper foil is laminated on one surface of a multilayer polyimide film, and a metal plate or ceramic plate with good heat transference is laminated on the other surface.